1. Field of the Invention
The present invention relates to a metal oxygen battery.
2. Description of the Related Art
Metal oxygen batteries have conventionally been known, which have a positive electrode using oxygen as an active substance, a negative electrode using a metal as an active substance, and an electrolyte layer interposed between the positive electrode and the negative electrode.
In the metal oxygen batteries, in the discharge time, a metal is oxidized to form metal ions at the negative electrode, and the formed metal ions migrate into the positive electrode side. On the other hand at the positive electrode, oxygen is reduced to form oxygen ions, and the formed oxygen ions bond with the metal ions to form a metal oxide. Further, in the charge time, at the positive electrode, the metal oxide formed by discharge is decomposed, and metal ions and oxygen ions are formed. The formed metal ions migrate into the negative electrode side. On the other hand, at the negative electrode the metal ions migrated into the negative electrode side are reduced and precipitated on the negative electrode.
In the metal oxygen battery, if metallic lithium is used as the metal, since the metallic lithium has a high theoretical potential and a large electrochemical equivalent weight, the metal oxygen battery can provide a large charge-discharge capacity. If oxygen in the air is used as the oxygen, since there is no need for filling a positive electrode active substance in a battery, the energy density per mass of the battery can be raised.
However, if the positive electrode is opened to the atmosphere in order to make oxygen in the air to be a positive electrode active substance, moisture, carbon dioxide and the like in the air invade in the battery, and there is caused a problem of deterioration of the electrolyte layer, the negative electrode and the like.
Then, in order to solve the problem, a metal oxygen battery is known, which has a positive electrode containing an oxygen-occluding material to release oxygen by reception of light, a negative electrode composed of metallic lithium, and an electrolyte layer disposed in a hermetically sealed case as a housing, and has a light transmission part to guide light to the oxygen-occluding material (for example, see Japanese Patent Laid-Open No. 2009-230985).
According, to the conventional metal oxygen battery equipped with the light transmission part, the metal oxygen battery can release oxygen from the oxygen-occluding material by guiding light to the oxygen-occluding material through the light transmission part, and can provide oxygen as a positive electrode active substance without exposing the positive electrode to the atmosphere. Therefore, the deterioration of the electrolyte layer, the negative electrode and the like due to the invasion of moisture, carbon dioxide and the like in the air into the battery can be prevented.
However, in the conventional metal oxygen battery, the supply of oxygen becomes unstable in the absence of irradiation of light rays, and there is a risk that the light transmission part, which is weaker than other pans of the hermetically sealed case, is broken and the electrolyte solution leaks out.
Then, it is conceivable that an oxygen-storing material which does not rely on irradiation of light rays and can occlude and release oxygen chemically, or adsorb and desorb oxygen physically is used as a positive electrode material of the metal oxygen battery. The oxygen-storing material is equipped with a function of occluding and releasing oxygen, and also is equipped with a function of adsorbing and desorbing oxygen on and from a surface thereof. Oxygen adsorbed on and desorbed from the surface of the oxygen-storing material is different from the oxygen occluded and released therefrom, and is not diffused in the oxygen storing material. Therefore, oxygen adsorbed on and resorbed from the surface of the oxygen-storing material is used for the balmy reaction with lower energy compared to the occluded and released oxygen, and it is conceivable that it acts favorably in the battery reaction.
In the metal oxygen battery, a typical usage is to start the use from discharge, however, it is conceivable to start the use from charging. In this case, in order to generate the decomposition reaction of the metal oxide at the positive electrode at the time of charging in the first cycle, it is conceivable to previously add the metal oxide to the positive electrode.
However, when starting use from charging in the metal oxygen battery equipped with a positive electrode including the oxygen-storing material and lithium oxide, and which is accommodated in a case, there is an inconvenience that charge-discharge overpotential is large, and sufficient batter capacity cannot not be obtained.